Summary
To follow changes in the status of phytochrome in green tissue and to relate these changes to the photoperiodic control of flowering, we have used a null response technique involving 1.5-min irradiations with mixtures of different ratios of R and FR radiation.
Following a main photoperiod of light from fluorescent lamps that was terminated with 5 min of R light, the proportion of Pfr in Chenopodium rubrum cotyledons was high and did not change until the 3rd hour in darkness; at this time, Pfr disappeared rapidly. When the dark period began with a 5-min irradiation with BCJ or FR light to set the proportion of Pfr low Pfr gradually reappeared during the first 3 h of darkness and then disappeared again.
The timing of disappearance of Pfr is consistent with the involvement of phytochrome in photoperiodic time measurement. Reappearance of Pfr after an initial FR irradiation explains why FR irradiations sometimes fail to influence photoperiodic time measurement or only slightly hasten time measurement. A R light interruption to convert Pr to Pfr delayed, the timer by 3 h but only for interruptions after and not before the time of Pfr disappearance. Such 5-min R-light interruptions did not influence the operation of the rhythmic timekeeping mechanism. Continuous or intermittent-5 min every 1.5 h-irradiations of up to 6 h in duration were required to rephase the rhythm controlling flowering. A skeleton photoperiod of 6 h that was began and terminated by 5 or 15 min of light failed to rephase the rhythm.
The shape of the curves for the rhythmic response of C. rubrum to the length of the dark period are sometimes suggestive of “clocks” operating on the principle of a tension-relaxation mechanism. Such a model allows for separate timing action of a rhythm and of Pfr disappearance over the early hours of darkness. Separate timing action does not, however, preclude an interaction between the rhythm and phytochrome in controlling flowering.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
Abbreviations
- FR:
-
far-red
- Pfr :
-
far-red-absorbing form of phytochrome
- Pr :
-
red-absorbing form of phytochrome
- R:
-
red
- BCJ:
-
photographic ruby-red irradiation
References
Akulovich, N. K., Godnev, T. N., Domash, V. I.: A method for determining phytochrome in green plants. Dokl. Akad. Nauk. Beloruss. SSR. 10, 601–603 (1966).
Boisard, J., Spruit, C. J. P., Rollin, P.: Phytochrome in seeds and an apparent dark reversion of Pr to Pfr. Meded. Landbouwhogeschool Wageningen 68, No. 17, 1–5 (1968).
Borthwick, H. A., Hendricks, S. B., Parker, M. W.: The reaction controlling floral initiation, Proc. nat. Acad. Sci. (Wash.) 38, 929–934 (1952).
Borthwick, H. A., Hendricks, S. B., Schneider, M. J., Taylorson, R. B., Toole, V. K.: The high-energy light action controlling plant responses and development. Proc. nat. Acad. Sci. (Wash.) 64, 479–486 (1969).
Butler, W. L., Lane, H. C., Siegelman, H.W.: Non photochemical transformations of phytochrome in vivo. Plant Physiol. 38, 514–519 (1963).
Cumming, B. G.: Evidence of a requirement for phytochrome-Pfr in the floral initiation of Chenopodium rubrum. Canad. J. Bot. 41, 901–926 (1963).
Cumming, B. G.: Photoperiodism and rhythmic flower induction: complete substitution of inductive darkness by light. Canad. J. Bot. 47, 1241–1250 (1969).
Cumming, B. G., Hendricks, S.B., Borthwick, H.A.: Rhythmic flowering responses and phytochrome changes in a selection of Chenopodium rubrum. Canad. J. Bot. 43, 825–853 (1965).
Denney, A., Salisbury, F. B.: Separate clocks for leaf movements and photoperiodic flowering in Xanthium strumarium L. (cocklebur). (Abstr.) Plant Physiol. 46, Suppl. 26 (1970).
Engelmann, W.: Endogene Rhythmik und photoperiodische Blühinduktion bei Kalanchoë. Planta (Berl) 55, 496–511 (1960).
Evans, L. T.: Flower induction and the florigen concept. Ann. Rev. Plant Physiol. 22, 365–394 (1971).
Evans, L. T., Hendricks, S. B., Borthwick, H. A.: The role of light in suppressing hypocotyl elongation in lettuce and Petunia. Planta (Berl) 64, 201–218 (1965).
Evans, L. T., King, R. W.: Role of phytochrome in photoperiodic induction of Pharbitis nil. Z. Pflanzenphysiol. 50, 277–288 (1969).
Grill, R., Vince, D.: Photocontrol of anthocyanin formation in turnip seedlings. VII. Phytochrome changes in darkness and on exposure to red and far-red light. Planta (Berl.) 89, 9–22 (1969).
Hendricks, S. B.: Rates of change of phytochrome as an essential factor determining photoperiodism in plants. Cold Spr. Harb. Symp. quant. Biol. 25, 245–248 (1960).
Hilman, W. S.: Entrainment of Lemna CO2 output through phytochrome Plant. Physiol. 48, 770–774 (1971).
Kasperbauer, M. J., Borthwick, H. A., Hendricks, S. B.: Reversion of phytochrome 730 (Pfr) to P660 (Pr) assayed by flowering in Chenopodium rubrum. Botan. Gaz. 125, 75–80 (1964).
Kendrick, R. E., Spruit, C. J. P., Frankland, B.: Phytochrome in seeds of Amaranthus caudatus. Planta (Berl.) 88, 293–302 (1969).
King, R. W.: Time measurement in the photoperiodic control of flowering. Doct. dissert., Univ. of Western Ontario, London, Canada (1971).
King, R. W., Cumming, B. G.: Rhythms as photoperiodic timers in the control of flowering in Chenopodium rubrum. Planta (Berl.) 103, 281–301 (1972).
Lang, A.: Physiology of flower initiation. In: Encycl plant physiol., vol. XV, pt. 1, p. 1380–1536, W. Ruhland, ed. Berlin-Heidelberg-New York: Springer 1965.
Nakayama, S.: Studies on the dark process in the photoperiodic response of Pharbitis seedlings. Sci. Rep. Tohoku Univ., Ser. IV, Biol. 24, 137–183 (1958).
Salisbury, F. B. Ross, C.: Plant physiology. Belmont, California: Wadsworth 1969.
Satter, R. L., Galston, A. W.: Phytochrome-controlled nyctinasty in Albizzia julibrissin. III. Interactions between an endogenous rhythm and phytochrome in control of potassium flux and leaflet movement. Plant Physiol. 48, 740–746 (1971).
Spruit, C. J. P., Mancinelli, A. L.: Phytochrome in cucumber seeds. Planta (Berl.) 88, 303–310 (1969).
Takimoto, A., Hamner K. C.: Effect of temperature and preconditioning on photoperiodic responses of Pharbitis nil. Plant Physiol. 39, 1024–1030 (1964).
Takimoto, A., Ikeda, K.: Studies on the light controlling flower initiation in Pharbitis nil. IV. Further studies on the light preceding the inductive dark period. Bot. Mag. (Tokyo) 93, 39–43 (1960).
Wagner, E., Cumming, B. G.: Betacyanin accumulation, chlorophyll content and flower initiation in Chenopodium rubrum, as related to endogenous, rhythmicity and phytochrome action. Canad. J. Bot. 48, 1–18 (1970).
Wetherell D. F.: Phytochrome in cultured wild carrot tissue. I. Synthesis. Plant Physiol. 44, 1734–1737 (1969).
Author information
Authors and Affiliations
Additional information
A grant in aid of research from the National Research Council of Canada to B. G. Cumming is gratefully acknowledged.
Rights and permissions
About this article
Cite this article
King, R.W., Cumming, B.G. The role of phytochrome in photoperiodic time measurement and its relation to rhythmic timekeeping in the control of flowering in Chenopodium rubrum . Planta 108, 39–57 (1972). https://doi.org/10.1007/BF00386505
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00386505